tty: Change tty lock order to master->slave

[deliverable/linux.git] / drivers / tty / tty_mutex.c

diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index 2e41abebbcbaef923c38a4ea6c3cee56dd6fe9fd..f43e995c7a0fc8a64ae1ee41eb2c7afa418df5b4 100644 (file)
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -4,6 +4,11 @@
 #include <linux/semaphore.h>
 #include <linux/sched.h>
 
+/*
+ * Nested tty locks are necessary for releasing pty pairs.
+ * The stable lock order is master pty first, then slave pty.
+ */
+
 /* Legacy tty mutex glue */
 
 enum {
@@ -45,29 +50,18 @@ void __lockfunc tty_unlock(struct tty_struct *tty)
 }
 EXPORT_SYMBOL(tty_unlock);
 
-/*
- * Getting the big tty mutex for a pair of ttys with lock ordering
- * On a non pty/tty pair tty2 can be NULL which is just fine.
- */
-void __lockfunc tty_lock_pair(struct tty_struct *tty,
-                                       struct tty_struct *tty2)
+void __lockfunc tty_lock_slave(struct tty_struct *tty)
 {
-       if (tty < tty2) {
-               tty_lock(tty);
-               tty_lock_nested(tty2, TTY_MUTEX_NESTED);
-       } else {
-               if (tty2 && tty2 != tty)
-                       tty_lock(tty2);
+       if (tty && tty != tty->link) {
+               WARN_ON(!mutex_is_locked(&tty->link->legacy_mutex) ||
+                       !tty->driver->type == TTY_DRIVER_TYPE_PTY ||
+                       !tty->driver->type == PTY_TYPE_SLAVE);
                tty_lock_nested(tty, TTY_MUTEX_NESTED);
        }
 }
-EXPORT_SYMBOL(tty_lock_pair);
 
-void __lockfunc tty_unlock_pair(struct tty_struct *tty,
-                                               struct tty_struct *tty2)
+void __lockfunc tty_unlock_slave(struct tty_struct *tty)
 {
-       tty_unlock(tty);
-       if (tty2 && tty2 != tty)
-               tty_unlock(tty2);
+       if (tty && tty != tty->link)
+               tty_unlock(tty);
 }
-EXPORT_SYMBOL(tty_unlock_pair);